PURPOSE: To reduce nonuniformity in exposure caused by nonuniformity in the film thickness of a Be film, by a method wherein a Be window fitted to an exposure zone and a beam line is shaken at a higher speed than the moving speed of a body to be exposed and a mask.

CONSTITUTION: A Be window 10 supporting a Be film 9 is disposed between a beam line 3 held on a route of an X-ray 1 radiated from a synchrotron orbit radiation(SOR) ring 2, and an exposure zone 5. The window 10 is fitted to the beam line 3 and the exposure zone 5 with bellows 11a and 11b interposed and it is shaken by a shaking device 12 in the horizontal direction intersecting the direction of movement of a semiconductor wafer W and a mask M perpendicularly. According to this constitution, nonuniformity in exposure in the horizontal direction for the wafer W is reduced by the shaking of the window 10 even when the film 9 has non-uniformity in a film thickness in the horizontal direction.